Removing nitrogen compounds from aromatic hydrocarbons by acid treatment



United States Patent Ofifice 3,052,742 Patented Sept. 4, 1962 REMOVING NITROGEN CQMPGUNDS FROM AROMATIC HYDRQCARBONS BY ACID TREATMENT Ivor W. Mills, Glenolden, Pa, assignor to Sun Oil Company, Philadelphia, Pan, a corporation of New Jersey No Drawing. Filed June 15, 1959, Ser. No. 820,117 4 Claims. (Ci. 260-6'74) The nitrogen compounds which occur in dicyclic aromatic hydrocarbon fractions obtained for example from petroleum or coal tar are often very refractory to removal by conventional acid treatment. The exact structure of the nitrogen compounds is not known, but their nature is such that ordinary acid treatment will often not remove an adequate amount of the nitrogen content of the hydrocarbon fraction.

It has now been found that a remarkable improvement in removal of nitrogen from such fractions is obtained if the fraction is hydrogenated under certain conditions and subsequently subjected to acid treatment. The hydrogenation in itself usually does not effect an adequate removal of nitrogen, but it apparently converts the nirogen compounds into a form in which they are readily removed by acid treating. The removal obtained with the combination of hydrogenation and acid treatment is superior to that obtainable by either treatment alone, and permits obtaining products having satisfactorily low nitrogen content, e.g. below 0.1 or even 0.05 Weight percent, from starting materials containing as much as one percent or more of nitrogen.

The starting material for the process of the invention comprises dicyclic aromatic hydrocarbons such as naphthalene, methyl naphthalenes, dimethyl naphthalenes, other alkyl naphthalenes, etc. Usually, the starting material contains compounds boiling at atmospheric pressure in the range from 240 to 270 C., though wider boiling fractions can be employed in some instances. The starting material may contain nonaromatic hydrocarbons, or it may be an aromatic concentrate substantially free of nonaromatic hydrocarbons. Usually, it will contain at least 25 weight percent of aromatic hydrocarbons, more frequently at least 50%.

The nitrogen compounds which are removed according to the invention are those which normally occur in such starting materials obtained either from petroleum or coal tar or other natural hydrocarbon source. The nitrogen compounds may be either compounds occurring naturally in the hydrocarbons, or compounds formed during conversion processes such as catalytic cracking of high boiling petroleum fractions, etc. Usually, the nitrogen content of the charge stock will be in the range from 0.01 to 1.5%, though charge stocks containing other amounts of nitrogen can satisfactorily be treated according to the invention.

The hydrogenation of the starting material is performed by contacting the hydrocarbon charge stock with hydrogen and a metallic hydrogenation catalyst. The temperature of the contacting is in the range from 650 to 925 F., and preferably in the range from 750 to 900 F. The pressure is preferably in the range from 250 to 1500 p.s.i.g., more preferably 250 to 750 p.s.i.g. These conditions provide a beneficial reduction in sulfur content as a result of the hydrogenation itself, and also provide a beneficial increase in the extent of nitrogen removal that can be obtained in a subsequent acid treating step. Also, conditions within these ranges can be chosen, by a person skilled in the art, which minimize the extent to which undesired reaction products are obtained, e.g. napthene-ring-containing hydrocarbons and monocyclic hydrocarbons.

The nature of the catalyst used is not critical, and any of the known catalysts for hydrogenation of petroleum or coal tar fractions can be employed. A particularly suitable catalyst is the well known catalyst comprising cobalt and molybdenum oxides on a porous carrier such as alumina, but others can be satisfactorily employed.

A preferred contacting procedure is to percolate the hydrocarbon in liquid phase through a stationary bed of the catalyst. Liquid hourly spaced velocities in the range from 0.25 to 5 are preferred, but others can be employed. In one embodiment, a film of trickling liquid hydrocarbon can be maintained on the catalyst surfaces, with hydrogen in the spaces between the catalyst particles. Any other contacting procedure, e.g. slurry contacting or other known techniques, can alternatively be employed.

Excess hydrogen and any gaseous products of the hy drogenation are separated from the aromatic hydrocarbons, and the separated gases can if desired be recycled to the hydrogenation, according to known procedures.

The aromatic hydrocarbons are then subjected to treatment with sulfuric acid in order to remove nitrogen compounds. The nature of the acid treatment is not critical, the hydrogenation having converted the nitrogen compounds into a fonm in which they are removable by any of the known acid treating techniques. Preferably, the concentration of the acid is at least in order to avoid corrosion, but lower concentrations can be used. Usually the concentration will be not greater than in order to avoid sulfonation of the hydrocarbons, though higher concentrations can be used in some instances.

The temperature of the acid treating is preferably in the range from room temperature to F., though other temperatures can be employed in some instances. Temperatures that are too high result in excessive side reactions. Petroleum and coal tar naphthalene and alkyl naphthalene fractions are usually sufiiciently fluid to be satisfactorily treated at such temperatures. Hydrocarbon diluents can be used to reduce the viscosity if desired. Such diluents can also be used in any case where the hydrocarbon charge is a normally solid material.

The amount of acid used is preferably in the range from 5 to 50 pounds per barrel, though other amounts can be used in some cases.

Following the acid treatment, known finishing procedures such as clay treatment, washing with Water or alkali etc., can be employed if desired, the procedure in this respect being conventional in acid treating.

The following examples illustrate the invention:

A mixture of methyl naphthalenes fractionated from cracked petroleum and containing 1.06 wt. percent of nitrogen and 0.67 wt. percent of sulfur is contacted with hydrogen and hydrogenation catalyst comprising about 20% of cobalt and molybdenum oxides on alumina at a temperature of 900 F. and a pressure of 500 p.s.i.g. The liquid space rate is 0.5 volume per volume per hour, and gaseous products are separated and recycled at a rate of 20,000 standard cubic feet per hour. The product obtained after separation of gases has an unsatisfactorily high nitrogen content, since it still contains 0.33 wt. percent of nitrogen, though its sulfur content has been reduced to 0.002 wt. percent.

The product is contacted at room temperature with 20 pounds per barrel of 98% sulfuric acid, and the acid is separated. The acid-treated product, after finishing with clay, contains only 0.02% nitrogen.

To determine the effect of the preceding hydrogenation, another sample of the same mixture is given a similar acid and clay treatment without the preceding hydrogenation. The product still contains more than half the original nitrogen content. Hydrogenation of this product under the above conditions produces a product still having unsatisfactorily high nitrogen content, indicating that it is necessary that the hydrogenation precede the acid treatment in order to obtain the beneficial results according to the invention.

The nitrogen removal according to the invention is useful in improving the color stability of heating oils containing dicyclic aromatics, and also of dicyclic aromatic concentrates obtained from such heating oils. It is also useful in improviding dicyclic aromatics and hydrocarbon fractions containing the same as charge stocks for known chemical processes, e.g. partial oxidation, for the conversion of the hydrocarbons to valuable products such as aromatic carboxylic acids.

The invention claimed is:

1. Process for removing nitrogen compounds from aro matic hydrocarbons which consists essentially of the steps of (1) contacting nitrogen containing dicyclic aromatic hydrocarbons selected from the group consisting of naphthalene and alkylnaphthalenes with hydrogen and a hydrogenation catalyst at a temperature of from 650 F. to 925 F., (2) contacting the hydrogenation product with at least percent sulfuric acid under conditions to remove normally liquid nitrogen compounds, and (3) separating the acid from the treated hydrocarbons.

2. Process according to claim 1 wherein the contact with hydrogen is at 750 to 900 F. and 250 to 750 p.s.i.g.

3. Process according to claim 1 wherein the temperature of contacting with acid is from room temperature to F, and the amount of acid used is 5 to 50 pounds of acid per barrel of hydrocarbons.

4. Process according to claim 3 wherein the hydrocarbons are subsequently clay treated.

References Cited in the file of this patent UNITED STATES PATENTS 1,999,738 Pier Apr. 30, 1935 2,920,115 Friedman Jan. 5, 1960 FOREIGN PATENTS 345,738 Great Britain Apr. 2, 1931 735,706 Great Britain Aug. 24, 1955 

1. PROCESS FOR REMOVING NITROGEN COMPOUNDS FROM AROMATIC HYDROCARBONS WHICH CONSISTS ESSENTIALLY OF THE STEPS OF (1) CONTACTING NITROGEN CONTAINING DICYCLIC AROMATIC HYDROCARBONS SELECTED FROM THE GROUP CONSISTING OF NAPHTHALENE AND ALKYLNAPHTHALENCES WITH HYDROGEN AND A HYDROGENATION CATALYST AT A TEMPERATURE OF FROM 650*F. TO 925*F., (2) CONTACTING THE HYDROGENATION PRODUCT WITH AT LEAST 80 PERCENT SULFURIC ACID UNDER CONDITIONS TO REMOVE NORMALLY LIQUID NITROGEN COMPOUNDS, AND (3) SEPARATING THE ACID FROM THE TREATED HYDROCARBONS. 